Earlier the primitive paddlefish
(Polyodon) entered the large reptile tree (LRT, 1634+ taxa) as the basalmost bony fish, distinct from and not related to traditional chondrostean relatives like the sturgeon (Psuedoschaphorhynchus), the bichir (Polypterus), and the extinct ‘chondrostean’ Chondrosteus.
Today, a baby paddlefish,
lacking a long paddle bill (Fig. 2), enters the LRT. Why? Because the paddle bill of the adult stands out as an autapomorphic trait in the cladogram, and I’m looking for plesiomorphic transitional taxa that link clades together. The short-snouted baby paddlefish (Fig. 2), looking just like a baby shark, but with an operculum, had the potential to do exactly that.
Despite the lack of an elongate rostrum
and the score changes that brings, the baby and adult Polyodon nest together in the LRT.
If ontogeny recapitulates phylogeny
in Polyodon, then the baby provides insight into the plesiomorphic morphology of a basalmost bony fish taxon, not far from a basalmost and transitional shark-clade taxa. That dichotomy likely extends back to the Late Silurian or Early Devonian. Thus, this long-sought and previously elusive mystery taxon might be best represented by a baby paddlefish. That means it was under our nose all along!
in the ‘old’ days, Polyodon used to be called the ‘paddle-bill catfish.’ Not sure when the common name change took place.
Grande L and Bemis WE 1991. Osteology and phylogenetic relationships of fossil and Recent paddlefishes (Polyodontidae) with comments on the interrelationships of Acipenseriformes. Society of Vertebrate Paleontology Memoir 1. Journal of Vertebrate Paleontology 11, Supplement to Number 1. 121pp.
Walbaum J 1792. Petri Artedi renovati. Part 3. Petri Artedi sueci genera Piscium in quibus systema totum ichthyologiae proponitur cum classibus, ordinibus, generum characteribus, specierum diffentiis, observationibus plumiris. Redactis Speciebus 2. Ichthyologiae, III: 723.